I have owned this car for two years now and recently it has a problem starting.

What happens:
The engines starts perfectly and runs for about 1 second and then shuts off automatically.
No matter how much gas I give the end result is the same. I have brought it to the garage and they can not find anything wrong with the car. The problem is that this occurs so sporadically that it is very difficult to trace down what might be causing this. When this happens it takes from 2-50 attempts to actually start the car. The sparkplugs have been changed. It has had annual service.

My guesses to what might be causing the problem:
-A faulty ignition switch
-faulty onboard computer (after starting the car a test is performed by pressing the brake pedal, when all is fine OK is displayed. my car continually displays "brems licht"-Brake lightly.

If any one has experienced this before or could point me in the right direction in what to check would be greatly appreciated.

Details of car:
1997 A4 Stationwagen (avant) 1.8T with 118,000 KM (+- 70,000 miles)

Regards,Alexander